aboutsummaryrefslogtreecommitdiff
path: root/qemu-bridge-helper.c
blob: 95624bc30055b9b5628e6cf495989b0f2ebb66d3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
/*
 * QEMU Bridge Helper
 *
 * Copyright IBM, Corp. 2011
 *
 * Authors:
 * Anthony Liguori   <aliguori@us.ibm.com>
 * Richa Marwaha     <rmarwah@linux.vnet.ibm.com>
 * Corey Bryant      <coreyb@linux.vnet.ibm.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 */

/*
 * Known shortcomings:
 * - There is no manual page
 * - The syntax of the ACL file is not documented anywhere
 * - parse_acl_file() doesn't report fopen() failure properly, fails
 *   to check ferror() after fgets() failure, arbitrarily truncates
 *   long lines, handles whitespace inconsistently, error messages
 *   don't point to the offending file and line, errors in included
 *   files are reported, but otherwise ignored, ...
 */

#include "qemu/osdep.h"


#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/prctl.h>

#include <net/if.h>

#include <linux/sockios.h>

#ifndef SIOCBRADDIF
#include <linux/if_bridge.h>
#endif

#include "qemu/queue.h"

#include "net/tap-linux.h"

#ifdef CONFIG_LIBCAP
#include <cap-ng.h>
#endif

#define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"

enum {
    ACL_ALLOW = 0,
    ACL_ALLOW_ALL,
    ACL_DENY,
    ACL_DENY_ALL,
};

typedef struct ACLRule {
    int type;
    char iface[IFNAMSIZ];
    QSIMPLEQ_ENTRY(ACLRule) entry;
} ACLRule;

typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;

static void usage(void)
{
    fprintf(stderr,
            "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
}

static int parse_acl_file(const char *filename, ACLList *acl_list)
{
    FILE *f;
    char line[4096];
    ACLRule *acl_rule;

    f = fopen(filename, "r");
    if (f == NULL) {
        return -1;
    }

    while (fgets(line, sizeof(line), f) != NULL) {
        char *ptr = line;
        char *cmd, *arg, *argend;

        while (g_ascii_isspace(*ptr)) {
            ptr++;
        }

        /* skip comments and empty lines */
        if (*ptr == '#' || *ptr == 0) {
            continue;
        }

        cmd = ptr;
        arg = strchr(cmd, ' ');
        if (arg == NULL) {
            arg = strchr(cmd, '\t');
        }

        if (arg == NULL) {
            fprintf(stderr, "Invalid config line:\n  %s\n", line);
            fclose(f);
            errno = EINVAL;
            return -1;
        }

        *arg = 0;
        arg++;
        while (g_ascii_isspace(*arg)) {
            arg++;
        }

        argend = arg + strlen(arg);
        while (arg != argend && g_ascii_isspace(*(argend - 1))) {
            argend--;
        }
        *argend = 0;

        if (strcmp(cmd, "deny") == 0) {
            acl_rule = g_malloc(sizeof(*acl_rule));
            if (strcmp(arg, "all") == 0) {
                acl_rule->type = ACL_DENY_ALL;
            } else {
                acl_rule->type = ACL_DENY;
                snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
            }
            QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
        } else if (strcmp(cmd, "allow") == 0) {
            acl_rule = g_malloc(sizeof(*acl_rule));
            if (strcmp(arg, "all") == 0) {
                acl_rule->type = ACL_ALLOW_ALL;
            } else {
                acl_rule->type = ACL_ALLOW;
                snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
            }
            QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
        } else if (strcmp(cmd, "include") == 0) {
            /* ignore errors */
            parse_acl_file(arg, acl_list);
        } else {
            fprintf(stderr, "Unknown command `%s'\n", cmd);
            fclose(f);
            errno = EINVAL;
            return -1;
        }
    }

    fclose(f);

    return 0;
}

static bool has_vnet_hdr(int fd)
{
    unsigned int features = 0;

    if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
        return false;
    }

    if (!(features & IFF_VNET_HDR)) {
        return false;
    }

    return true;
}

static void prep_ifreq(struct ifreq *ifr, const char *ifname)
{
    memset(ifr, 0, sizeof(*ifr));
    snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
}

static int send_fd(int c, int fd)
{
    char msgbuf[CMSG_SPACE(sizeof(fd))];
    struct msghdr msg = {
        .msg_control = msgbuf,
        .msg_controllen = sizeof(msgbuf),
    };
    struct cmsghdr *cmsg;
    struct iovec iov;
    char req[1] = { 0x00 };

    cmsg = CMSG_FIRSTHDR(&msg);
    cmsg->cmsg_level = SOL_SOCKET;
    cmsg->cmsg_type = SCM_RIGHTS;
    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
    msg.msg_controllen = cmsg->cmsg_len;

    iov.iov_base = req;
    iov.iov_len = sizeof(req);

    msg.msg_iov = &iov;
    msg.msg_iovlen = 1;
    memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));

    return sendmsg(c, &msg, 0);
}

#ifdef CONFIG_LIBCAP
static int drop_privileges(void)
{
    /* clear all capabilities */
    capng_clear(CAPNG_SELECT_BOTH);

    if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
                     CAP_NET_ADMIN) < 0) {
        return -1;
    }

    /* change to calling user's real uid and gid, retaining supplemental
     * groups and CAP_NET_ADMIN */
    if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
        return -1;
    }

    return 0;
}
#endif

int main(int argc, char **argv)
{
    struct ifreq ifr;
#ifndef SIOCBRADDIF
    unsigned long ifargs[4];
#endif
    int ifindex;
    int fd = -1, ctlfd = -1, unixfd = -1;
    int use_vnet = 0;
    int mtu;
    const char *bridge = NULL;
    char iface[IFNAMSIZ];
    int index;
    ACLRule *acl_rule;
    ACLList acl_list;
    int access_allowed, access_denied;
    int ret = EXIT_SUCCESS;

#ifdef CONFIG_LIBCAP
    /* if we're run from an suid binary, immediately drop privileges preserving
     * cap_net_admin */
    if (geteuid() == 0 && getuid() != geteuid()) {
        if (drop_privileges() == -1) {
            fprintf(stderr, "failed to drop privileges\n");
            return 1;
        }
    }
#endif

    /* parse arguments */
    for (index = 1; index < argc; index++) {
        if (strcmp(argv[index], "--use-vnet") == 0) {
            use_vnet = 1;
        } else if (strncmp(argv[index], "--br=", 5) == 0) {
            bridge = &argv[index][5];
        } else if (strncmp(argv[index], "--fd=", 5) == 0) {
            unixfd = atoi(&argv[index][5]);
        } else {
            usage();
            return EXIT_FAILURE;
        }
    }

    if (bridge == NULL || unixfd == -1) {
        usage();
        return EXIT_FAILURE;
    }

    /* parse default acl file */
    QSIMPLEQ_INIT(&acl_list);
    if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
        fprintf(stderr, "failed to parse default acl file `%s'\n",
                DEFAULT_ACL_FILE);
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* validate bridge against acl -- default policy is to deny
     * according acl policy if we have a deny and allow both
     * then deny should always win over allow
     */
    access_allowed = 0;
    access_denied = 0;
    QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
        switch (acl_rule->type) {
        case ACL_ALLOW_ALL:
            access_allowed = 1;
            break;
        case ACL_ALLOW:
            if (strcmp(bridge, acl_rule->iface) == 0) {
                access_allowed = 1;
            }
            break;
        case ACL_DENY_ALL:
            access_denied = 1;
            break;
        case ACL_DENY:
            if (strcmp(bridge, acl_rule->iface) == 0) {
                access_denied = 1;
            }
            break;
        }
    }

    if ((access_allowed == 0) || (access_denied == 1)) {
        fprintf(stderr, "access denied by acl file\n");
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* open a socket to use to control the network interfaces */
    ctlfd = socket(AF_INET, SOCK_STREAM, 0);
    if (ctlfd == -1) {
        fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* open the tap device */
    fd = open("/dev/net/tun", O_RDWR);
    if (fd == -1) {
        fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* request a tap device, disable PI, and add vnet header support if
     * requested and it's available. */
    prep_ifreq(&ifr, "tap%d");
    ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
    if (use_vnet && has_vnet_hdr(fd)) {
        ifr.ifr_flags |= IFF_VNET_HDR;
    }

    if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
        fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* save tap device name */
    snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);

    /* get the mtu of the bridge */
    prep_ifreq(&ifr, bridge);
    if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
        fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
                bridge, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* save mtu */
    mtu = ifr.ifr_mtu;

    /* set the mtu of the interface based on the bridge */
    prep_ifreq(&ifr, iface);
    ifr.ifr_mtu = mtu;
    if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
        fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
                iface, mtu, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* Linux uses the lowest enslaved MAC address as the MAC address of
     * the bridge.  Set MAC address to a high value so that it doesn't
     * affect the MAC address of the bridge.
     */
    if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
        fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
                iface, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }
    ifr.ifr_hwaddr.sa_data[0] = 0xFE;
    if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
        fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
                iface, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* add the interface to the bridge */
    prep_ifreq(&ifr, bridge);
    ifindex = if_nametoindex(iface);
#ifndef SIOCBRADDIF
    ifargs[0] = BRCTL_ADD_IF;
    ifargs[1] = ifindex;
    ifargs[2] = 0;
    ifargs[3] = 0;
    ifr.ifr_data = (void *)ifargs;
    ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
#else
    ifr.ifr_ifindex = ifindex;
    ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
#endif
    if (ret == -1) {
        fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
                iface, bridge, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* bring the interface up */
    prep_ifreq(&ifr, iface);
    if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
        fprintf(stderr, "failed to get interface flags for `%s': %s\n",
                iface, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    ifr.ifr_flags |= IFF_UP;
    if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
        fprintf(stderr, "failed to bring up interface `%s': %s\n",
                iface, strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* write fd to the domain socket */
    if (send_fd(unixfd, fd) == -1) {
        fprintf(stderr, "failed to write fd to unix socket: %s\n",
                strerror(errno));
        ret = EXIT_FAILURE;
        goto cleanup;
    }

    /* ... */

    /* profit! */

cleanup:
    if (fd >= 0) {
        close(fd);
    }
    if (ctlfd >= 0) {
        close(ctlfd);
    }
    while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
        QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
        g_free(acl_rule);
    }

    return ret;
}